A gasoline engine, which is gasoline-fueled, has been widely used as a source of power for driving an automobile. A mixture of gasoline, which is main fuel, and air is generally burned to put the gasoline engine into motion. In recent years, however, efforts have been made to commercialize a technology for adding hydrogen to the above air-fuel mixture.
It is also estimated that hydrogen will be increasingly used as automotive fuel not only in gasoline engines, diesel engines, hydrogen engines, and other internal combustion engines, but also in fuel cells for use in an electric automobile and other hydrogen-powered apparatuses other than engines.
In reality, however, the technology concerning a hydrogen supply method is still not established. Therefore, when hydrogen is to be supplied to an internal combustion engine, fuel cell, or the like, it is necessary that the vehicle carry hydrogen or hydrogen-generating raw fuel. More specifically, when the vehicle is to carry hydrogen, hydrogen-rich gas is compressed to a high-pressure gas or liquefied and filled into a steel cylinder (e.g., high-pressure tank or liquid hydrogen tank). An alternative is to use a hydrogen storage alloy or hydrogen adsorption material for storing hydrogen. When the vehicle is to carry raw fuel, the vehicle incorporates methanol, gasoline, or other hydrocarbon as the raw fuel and a hydrogen generator for generating hydrogen-rich gas by steam-reforming the raw fuel.
However, if the vehicle carries hydrogen that is compressed into a high-pressure tank, the hydrogen storage amount is small because the high-pressure tank has a thick wall and cannot provide an adequate inner volume although the tank is large. If the vehicle carries liquid hydrogen, the overall energy efficiency is not high because it entails a vaporization loss and requires a large amount of energy for liquefaction. If the hydrogen storage alloy or hydrogen adsorption material is used, the resulting hydrogen storage density is inadequate and it is very difficult to control hydrogen storage and adsorption. It is also necessary to furnish facilities for compressing, liquefying, and storing hydrogen.
Meanwhile, when the vehicle carries raw fuel, a single fuel refill provides a longer traveling distance than the use of hydrogen. Hydrocarbon raw fuel can be transported and otherwise handled more easily than the hydrogen-rich gas. Further, when hydrogen burns, it combines with oxygen in the air to form water, thereby presenting no environmental pollution hazard.
Decalin (decahydronaphthalene), which is one of hydrocarbon raw fuel, for example, can be handled easily because the vapor pressure is approximately zero at normal temperature (the boiling point is approximately 200° C.). Therefore, decalin is highly expected to be used as raw fuel.
In a known method for dehydrogenating decalin, decalin is irradiated with light in the presence of a transition metal complex including at least one transition metal that is selected from among cobalt, rhodium, iridium, iron, tellurium, nickel, and platinum (refer, for instance, to Patent Document 1). In a known method for producing hydrogen from decalin, decalin is irradiated with light in the presence of a rhodium complex, which is an organic phosphorous compound, or in the presence of an organic phosphorous compound and rhodium compound (refer, for instance, to Patent Document 2). Decalin dehydrogenation occurs as indicated below:C10H18(decalin)→C10H8(naphthalene)+5H2(hydrogen)
A hydrogen fuel supply system that uses decalin, cyclohexane, or other organic hydride as raw fuel is also disclosed (refer, for instance, to Patent Documents 3 and 4).    [Patent Document 1]    Japanese Patent Publication No. 9091/1991    [Patent Document 2]    Japanese Patent Publication No. 18761/1993    [Patent Document 3]    Japanese Patent Laid-Open No. 110437/2001    [Patent Document 4]    Japanese Patent Laid-Open No. 255503/2002